I did not see the GMH9 with the Glock lower, but both APC 9 and GMH9 use the same lower.
I don't think the B&T USA people at the booth are 100% sure how these things will be sold or what exactly they are going to do with various configurations. But B&T at USA is not the same as B&T itself in Switzerland.
Personally , I much prefer a Glock lowered GMH9. The APC9 is a bit too big and heavy for 9mm SMG. GMH9 is what this kind of firearms should look like.